World’s largest ocean has never been seen

The discovery of water molecules buried within blue ringwoodite, which is found hundreds of miles inside the Earth, may be empirical evidence that the world's largest ocean is subterranean. Photo credit: Jasperox.
The discovery of water molecules buried within blue ringwoodite, which is found hundreds of miles inside the Earth, may be empirical evidence that the world’s largest ocean is subterranean. Photo credit: Jasperox.

By Rachel Sloan

The biggest ocean in the world has never been seen, according to scientists who discovered a massive ocean under North America that could be the source of all the surface water on Earth.

The origin of Earth’s water has long been debated. For decades, the prevailing theory was that the planet formed as a hot, dry orb with a molten surface that instantly evaporated any water that touched it. As the Earth slowly cooled, collisions with ice-bearing asteroids and meteors brought the water that formed the oceans, according to the theory.

That theory was widely accepted until 2014 when Adam Sarafin and his colleagues at the Woods Hole Oceanographic Institute (WHOI) discovered convincing evidence that water existed on Earth from the very beginning, approximately 4.6 billion years ago.

“The planet formed as a wet planet with water on the surface,” said Horst Marshall, one of Sarafin’s co-authors.

And yet, it seems the mystery was not completely solved after all. Geophysicist Steven Jacobsen of Northwestern University partnered with Brandon Schmandt, a seismologist from the University of New Mexico, to study the speed of seismic waves as they move through the Earth. The two scientists observed that the waves slowed as they hit a layer of a mineral called ringwoodite deep in the mantle. This slowing indicates that the mineral is saturated with water, evidence for the existence of many oceans’ worth of saltwater deep within the planet.

Ringwoodite is a crystalline form of the mineral olivine, formed under high pressure and only found between 325 and 400 miles beneath the Earth’s surface. In laboratory tests, Jacobsen and Schmandt found that ringwoodite attracts hydrogen and can actually absorb water. That discovery has led scientists to conclude that an underground ocean is unlikely to have waves. In fact, the enormous water deposit in the Earth wouldn’t resemble an ocean at all, rather it’s more likely to be an enormous sea of water trapped within rock.

Scientists explained in a Live Science interview that many ocean rocks are similarly saturated with water, according to other studies. Rocks sitting on the ocean floor can contain up to 15 percent water, trapped within the molecular structure of the stone. If only one percent of the ringwoodite in the mantle is water, that would mean the underground reservoir holds three times the amount of salt water presently circulating in the five oceans.

Researchers believe that the discovery of this underground ocean provides evidence that Earth’s surface water originated within the planet itself.

“I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet,” Jacobsen said.